University of Crete HEP Seminars


FP7

Higher form symmetries and superfluids

Speaker: Diego Hofman
Institution: University of Amsterdam
Time: Monday 23 September 2019, 14:15
Venue: 2nd floor seminar room
Abstract: I will describe superfluid hydrodynamics as the hydrodynamic theory of a system with an emergent anomalous higher-form symmetry. The higher-form charge counts the winding planes of the superfluid -- its constitutive relation replaces the Josephson relation of conventional superfluid hydrodynamics. This formulation puts all hydrodynamic equations on equal footing. The anomalous Ward identity can be used as an alternative starting point to prove the existence of a Goldstone boson, without reference to spontaneous symmetry breaking. This provides an alternative characterization of Landau phase transitions in terms of higher-form symmetries and their anomalies instead of how the symmetries are realized. This treatment is more general and, in particular, includes the case of BKT transitions.

Dark matter search and gravitational wave detection using atom interferometry

Speaker: Wolf von Klitzing
Institution: IESL-FORTH Crete
Time: Thursday 26 September 2019, 14:15
Venue: 2nd floor seminar room
Abstract: In a recent White Paper (arXiv:1908.00802) we proposed a concept for a space experiment using cold atoms to search for ultra-light dark matter, and to detect gravitational waves in the frequency range between the most sensitive ranges of LISA and the terrestrial LIGO/Virgo/KAGRA/INDIGO experiments. This interdisciplinary experiment, called Atomic Experiment for Dark Matter and Gravity Exploration (AEDGE), will also complement other planned searches for dark matter, and exploit synergies with other gravitational wave detectors. We give examples of the extended range of sensitivity to ultra- light dark matter offered by AEDGE, and how its gravitational-wave measurements could explore the assembly of super-massive black holes, first-order phase transitions in the early universe and cosmic strings. AEDGE will be based upon technologies now being developed for terrestrial experiments using cold atoms (also on Crete), and will benefit from the space experience obtained with, e.g., LISA and cold atom experiments in microgravity.

The Geometric Trinity of Gravity: the TEGR case

Speaker: Konstantinos Dialektopoulos
Institution: Center for Gravitation and Cosmology, Yangzhou University
Time: Friday 27 September 2019, 16:15
Venue: 2nd floor seminar room
Abstract: It is well established by now that General Relativity and the LCDM model are very successful in describing the gravitational interactions at all scales. However, the theory is plagued with some shortcomings, enabling scientists to pursue an alternative formulation of gravity. In this talk, I am going to review the three different formulations of gravity; one based on the curvature of spacetime (General Relativity), one based on its torsion (Teleparallel Equivalent of General Relativity, TEGR) and one based on its non-metricity (Symmetric Teleparallel of General Relativity, STEGR). I will try to focus on the TEGR, explaining some of its key features.

Fine Tuning Problems from Cosmological Coleman-Weinberg Potentials

Speaker: Richard Woodard and S.P. Miao
Institution: UF (USA) and NCKU (Taiwan)
Time: Monday 21 October 2019, 14:15
Venue: 2nd floor seminar room
Abstract: Cosmological Coleman-Weinberg potentials are quantum corrections to the effective potential of the inflaton which result from coupling it to ordinary matter in order make re-heating efficient. These corrections are problematic for inflation because they are not Planck-suppressed and tend to make the potential too steep. Therefore they must be subtracted off by additions to the classical action. Unfortunately, they cannot be completely subtracted off. Although they go over to the Coleman-Weinberg form in the flat space limit, their actual form on de Sitter background is the 4th power of the Hubble parameter times a complicated function of the coupling constant times the ratio of the inflaton to the Hubble parameter. On a general inflationary background they are not even local functions of the geometry, whereas the allowable subtractions consist of algebraic functions of the inflaton and the Ricci scalar. We discuss the disturbing results from the best possible local subtraction schemes. This talk is based on arXiv:1506.07306, 1806.02533, 1908.03814 and 1908.05558.

Comments on the black hole S-matrix

Speaker: Panagiotis Betzios
Institution: UOC
Time: Tuesday 5 November 2019, 14:15
Venue: 2nd floor seminar room
Abstract: I will review the shockwave construction of 't Hooft by which gravitational backreaction can lead to a unitary S-matrix for particles scattering on an eternal black hole background. In order to obtain a background with a single exterior, an antipodal (CPT) identification was recently proposed that could in principle give a resolution to the information paradox for single sided asymptotically flat black holes. An emphasis will be given in the various assumptions and caveats of this construction. I will then describe an explicit dynamical quantum mechanical system that results in the same S-matrix. If time permits I will conclude with some efforts towards understanding the experience of an infalling observer in this setup.

The Skyrmion Paradox

Speaker: Christos Panagopoulos
Institution: NTU Singapore
Time: Tuesday 12 November 2019, 14:15
Venue: 2nd floor seminar room
Abstract: Magnetic skyrmions (or vortices) are spatially inhomogeneous spin textures localized in nanoscale cylindrical regions. Topological protection and small size make skyrmions especially attractive for the study of spin topology and technologies wherein information is carried by the electron spin further to, or instead of the electron charge. Despite achievements in the synthesis of materials where axisymmetric magnetic skyrmions can be stabilized and characterized, there is disproportionate progress in elucidating the basic properties. The talk will attempt to bridge this gap and deliver an intelligible guide on the physical principles governing these magnetic whirls.

Bootstrapping three dimensional cubic theories

Speaker: Stefanos Kousvos
Institution: UOC
Time: Thursday 14 November 2019, 14:15
Venue: 2nd floor seminar room
Abstract: After a concise introduction to the conformal bootstrap in general dimensions, I will discuss recent results regarding theories with cubic global symmetry in three spatial dimensions. Under certain assumptions, we find an isolated region in parameter space, which given prior intuition with the numerical conformal bootstrap, hints towards the existence of a CFT in this region of parameter space. We study the consistency of this CFT using multiple correlator systems. We find critical exponents for the conjectured CFT which are in discrepancy with the epsilon expansion (but in agreement with experiments for structural phase transitions). The disagreement of critical exponents for structural phase transitions calculated in the epsilon expansion with those measured in experiments is something that was noticed since the 70s. Given time I will briefly mention a resolution to this apparent discrepancy proposed at that time.

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Speaker: Spyros Sotiriadis
Institution: University of Ljubljana
Time: Tuesday 4 February 2020, 14:15
Venue: 2nd floor seminar room
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Speaker: Georgios Papathanasiou
Institution: DESY
Time: Thursday 6 February 2020, 14:15
Venue: 2nd floor seminar room
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Speaker: Pascal Anastasopoulos
Institution: Vienna University
Time: Tuesday 11 February 2020, 14:15
Venue: 2nd floor seminar room
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Speaker: Severin Lust
Institution: Ecole Polytechnique
Time: Tuesday 25 February 2020, 14:15
Venue: 2nd floor seminar room
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Speaker: Alejandro Cabo-Bizet
Institution: KCL London
Time: Tuesday 03 March 2020, 14:15
Venue: 2nd floor seminar room
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Speaker: Elli Pomoni
Institution: DESY
Time: Thursday 05 March 2020, 14:15
Venue: 2nd floor seminar room
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Speaker: Diego Rodriguez-Gomez
Institution: University of Oviedo
Time: Tuesday 24 March 2020, 14:15
Venue: 2nd floor seminar room
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Speaker: Konstantinos Siampos
Institution: UOA
Time: Tuesday 31 March 2020, 14:15
Venue: 2nd floor seminar room
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Speaker: Konstantinos Siampos
Institution: UOA
Time: Thursday 02 April 2020, 14:15
Venue: 2nd floor seminar room
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Speaker: Aristomenis Donos
Institution: Durham University
Time: Tuesday 07 April 2020, 14:15
Venue: 2nd floor seminar room
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Speaker: Matteo Baggioli
Institution: IFT, Madrid
Time: Thursday 09 April 2020, 14:15
Venue: 2nd floor seminar room
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Speaker: Nicholas Warner
Institution: University of Southern California
Time: Tuesday 05 May 2020, 14:15
Venue: 2nd floor seminar room
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